Nick - Below are extracts from the 1946 (Art Deco) Chevy frame specs (1st pic) and the 1947 (AD) frame specs (2nd pic). Not a ton of difference in the rear overall width with the '41-'46 being 46" wide over all and the '47 being 46-1/32" wide overall. Age "spread" could make your 46-3/16" either one. The big difference to help decide if an Art Deco or AD frame is the overall length. 1941-46 Art Deco 1/2 tons are listed as 171-7/8" overall, while the 1947 AD 1/2 ton is 173-1/8" overall. Not a significant difference, but enough I think to help you pin down which frame you have.
Since the 1939-40 Light Delivery 1/2 ton trucks used the same rear frame width of 46" as the 1941-46, I think you should be able to use a 1940 rear bumper with minimal modifications on your frame.
This is all based on my reading of the dimensions found in the
GM Heritage Center Vehicle Information Kits. Others with more hands on experience will likely chime in with their thoughts and input soon.
